Control system for mutiple driving axle vehicle

ABSTRACT

In multiple driving axle vehicles, such as four wheel drive automotive vehicles, drive is transmitted to front and rear differentials respectively drivingly connected to front and rear pairs of road wheels, a controlled third or center differential drivingly connected to the front and rear differentials and acting as a free differential until one output of this differential rotates slower or faster a predetermined amount than the other output, at which time the control acts to operate a clutch to lock the center differential preventing any further increase in speed differences. The control is sensitive to the speed differences, percentagewise, of the outputs of the front and rear differentials, and acts to bias torque in the third differential according to the derivative of their speeds.

United States Patent [1 1 Shiber July 31, 1973 CONTROL SYSTEM FORMUTIPLE Primary ExqminerMcKeo n Arthur 1.

DRIVING AXLE VEHICLE Attorney-Donald W. Banner, Robert L. Zieg et al.

[75] Inventor: Samuel ShIber, Chicago, Ill. ABSTRACT [73] Assgnee:Bm'g'wamer Corporation Chlcago, In multiple driving axle vehicles, suchas four wheel drive automotive vehicles, drive is transmitted to front22 Filed; Sept 20 1971 and rear differentials respectively drivinglyconnected Appl. No.: 181,928

to front and rear pairs of road wheels, a controlled third or centerdifferential drivingly connected to the front and rear differentials andacting as a free differential until one output of this difierentialrotates slower or faster a predetermined amount than the other output,at which time the control acts to operate a clutch to lock the centerdifferential preventing any further increase in speed differences. Thecontrol is sensitive to the speed difierences, percentagewise, of theoutputs of the front and rear differentials, and acts to bias torque inthe third differential according to the derivative of their speeds.

22 Claims, 11 Drawing Figures Patented July 31, .1973

4 Sheets-Sheet l INVENTOQ SAW/V51 57/455? BY M ATTO RN EV Patented July31, 1973 3,748,928

4 Sheets-Sheet 5 NVENTOR SAMUEL SH/EEQ BY 0W M h/Jnm ATTORNEY PatentedJuly 31, 1973 3,748,928

4 Sheets-Sheet 4 I N v E N TO R SAMVEZ 5/0552 BY DM ATTO RN EV CONTROLSYSTEM FOR MUTIPLE DRIVING AXLE VEHICLE BACKGROUND AND SUMMARY OF THEINVENTION This invention relates to multiple driving axle vehicles, suchas four wheel drive automotive vehicles, and more particularly tocontrol systems for positively limiting the differential action ofdifferential gearing of such vehicles to predetermined limits.

It is well known that four wheel drive automotive vehiclesconventionally employ front and rear driving axles having front and reardifferentials respectively drivingly connected to front and rear pairsof road wheels through a third or controlled differential powered by theengine. Such controlled differential functions to prevent or hinderspinning of one driving axle relative to the other dirving axle. In US.Pat. No. 2,796,941, a control, proposed for providing this function, isautomatically operative and is adapted for use with a centerdifferential having a planet carrier driven by the engine and havingfirst and second sun gears, gears respectively connecting the first andsecond sun gears to the front and rear drive shafts with speed changeratios such that the second sun gear rotates a predetermined percentagefaster than the planet carrier when the front and rear pairs of wheelsare driven at the same angular speed, with a first two-way overrunningclutch connected between the front wheel and rear wheel drive shafts tolock them upon overspeeding of the rear drive shaft relative to thefront drive shaft resulting in a positive drive to the front wheelsthrough the first clutch, and a second two-way overrunning clutchconnected between the planet carrier and the second sun gear to lockthem upon overspeeding of the planet carrier and front wheels relativeto the second sun gear and rear wheels providing a positive drive to therear wheels through the second clutch. In this control, different andalternate drive paths between the front wheels and rear wheels areprovided by the respective one-way clutches, which are instrumental intransmitting torque between the drive and driven shafts, dependent onoverspeeding one or the other of the shafts. It will be apparent suchcontrol is automatically operative dependent on and sensitive only tothe nominal speed ratio between the two differential outputs.

The present invention is directed to, and has for its principal object,an improved control system for the third or center differential of afour wheel drive automotive vehicle and which control system ischaracterized by being sensitive to the speed ratio, percentagewise, ofthe rotary speed of an input shaft and two output shafts and, uponsensing more than a predetermined speed difference between any twoshafts, to bias torque across the third differential.

Another object of the invention is to provide an improved control systemfor a differential having three interconnected shafts and includingmeans responsive to the speed differences of two shafts and effective todivide their speeds to provide a speed ratio generating a signal foractivating torque-biasing means operative to limit the speed ratio ofthe two shafts below or above a predetermined value.

Another object of the invention is to provide a control system for adifferential having an input shaft and two output shafts, and includingmeans energizable to bias torque across the third differential and meanssensing the rotary speeds of the shafts and operative to energize thetorque biasing means upon sensing more than a predetermined speeddifference between any two shafts.

Another object of the invention is to provide an improved control systemfor a differential having an input shaft and two output shafts, ahydraulic clutch operable to bias torque between the shafts for conjointrotation, a valve actuatable to supply fluid pressure to the clutch, andmeans sensing the rotary speeds of the shafts and operative, upon speeddifferences between the output shafts, to actuate the valve.

Additional objects and advantages will be apparent from the followingdetailed description taken in conjunction with the drawings.

DESCRIPTION OF TI-IE DRAWINGS FIG. 1 is a diagrammetric top plan view ofa four wheel drive motor vehicle and embodying a controlled centerdifferential of the present invention;

FIG. 2 is an enlarged, partial sectional view of the differential shownin FIG. 1;

FIG. 3 is a transverse fragmental sectional view taken on line 3-3 ofFIG. 2;

FIG. 4 is a transverse fragmental sectional view taken on line 4-4 ofFIG. 2;

FIG. 5 is an enlarged partial sectional fragmentary view illustrating afirst modified embodiment of the differential control shown in FIG. 2;

FIG. 6 is a fragmentary partial view of the pressure fluid supply valvefor the hydraulic clutch of the differential control embodiment of FIG.5;

FIG. 7 is an enlarged partial sectional fragmenta view illustrating asecond modified embodiment of .the differential control shown in FIG. 2;

FIG. 8 is a view similar to FIG. 2 and showing a third modifiedembodiment of the invention;

FIG. 9 is a vertical sectional view taken on line 9-9 of FIG. 8;

FIG. 10 is a view similar to FIG. 2 but illustrating a fourth modifiedembodiment;

FIG. 11 is a schematic plan view of a four wheel drive vehicle embodyingthe differential and control system therefor shown in FIG. 10.

DESCRIPTION OF EMBODIMENT OF THE INVENTION OF FIGS. 1, 2, 3 AND 4Referring to FIG. 1 of the drawings, there is shown a four wheel driveautomotive vehicle having front and rear pairs of road wheels 10 and 12,respectively, first and second drive shafts in the, form of frontandrear propeller shafts l4 and 16, respectively, front and reardifferentials 18 and 20, respectively, an engine 22, and transmissionmeans provided by a center or third differential and drive transfer unit24 providing a driving connection between the engine 22 and the frontand rear propeller shafts l4 and 16. A disengageable friction clutch 26and a change-speed gear box 28 are drivingly interposed between theengine 22 and the unit'2 4, the gearbox output being connected to aninput or-first transmission shaft 30 (see FIG. 2) in the unit 24by' arelatively short connecting shaft 32, having universal joints 34 and 36represented diagrammatically in FIG. 1. The front and rear propellershafts l4 and 16 incorporate universal joints 38, 40, 42,, 44respectively.

With the exception of the center differential and drive transfer unit24, the purpose and operation of the other parts of the vehicle whichare mentioned above are well known and the following description andoperation of the unit 24 is made with reference mainly to FIGS. 2, 3,and 4.

The components of the unit 24 are housed in a separate casing 46 andcomprise, generally, a center differential gear set 48, the firsttransmission input shaft 30, a second transmission or output shaft 50, athird transmission sleeve shaft 52, a fourth transmission shaft 53,drive transfer means 54 and 56, a fluid-actuated device in the form ofan hydraullically operated friction clutch S8, operative to bias torquebetween two of said shafts and control means sensing speed ratio betweentwo of said shafts for activating the clutch in response to said speedratio being in excess of a predetermined value and including overrunningclutch devices 60 and 62, and a valve 64 controlling pressure fluid toclutch 58.

The center differential comprises a planetary gear set 48 having threeelements, namely, a sun gear 66, an annulus or ring gear 68, and aplanet carrier 70 carrying planet gears 72-, only one of which is shownin FIG. 2. Each planet gear 72 meshes with the sun and ring gears 66 and68. The gear teeth of the ring gear 68 are formed internally on theinner surface of a cylindrical portion 74 of a cup-shaped member 76which has an integrally formed stern portion providing the transmissionshaft 53 and a part of which is rotatably supported in the casing 46 bya bearing 80. The stem portion or transmission shaft 53 isspline-connected to the universal joint 42 and is thus drivinglyconnected to the rear pair of road wheels 12,12 by the propeller shaft16, universal joint 44 and rear differential 20.

The transmission shaft 30 is positioned coaxially with the centerdifferential gear set 48 and is rotatably supported in and by thetransmission sleeve shaft 52, the rear end of shaft 30 extending intoand being rotatable on a bearing 82 located in a bore in the stemportion 74 of cup-shaped member 76. The planet carrier 70 is formedintegral with and extends radially outward of the shaft 30 between theend of sleeve shaft 52 and the cup-shaped member 76. The sleeve shaft 52is rotatably supported near its forward end in the casing 46 by abearing 84 mounted in a wall 86 of casing 46 and is provided with teethat its rear end forming the sun gear 66.

The second transmission shaft 50 is spaced laterally from and parallelto the shaft 30 and is rotatably supported in the casing 46 by bearings88 and 90. A forward extension 92 of the shaft 50 is key connected tothe universal joint 38 and is thus drivingly connected to the front pairof road wheels 10,10 by way of the propeller shaft 14, universal joint40 and front differential 18.

The drive transfer means between the second shaft 50 and third shaft 52are provided by the pair of meshing toothed elements or gears 54 and 56,the gear 54 being secured to and coaxial with the sleeve shaft 52 andthe gear 56 being secured to and coaxial with shaft 50.

The friction clutch 58 comprises a set of mutually interleaved frictionplates 94 and 96 respectively associated with the cylindrical portion 74of the cup-shaped member 76 and the sleeve shaft 52. The friction plates94 are carried in axial slots formed in the inner surface of thecylindrical portion 74, the slots being continuations of slots in theportion 74 defining the teeth of the ring gear 68. The plates 94 havetheir outer peripheral edges provided with radial tongues forcooperation with the slots in cylindrical portion 74 so that the platesrotate with the cup-shaped member 76 and are freely axially movablerelative thereto. The friction plates 96 have their inner peripheraledges provided with radial tongues received within axial slots formed inthe outer surface of the sleeve shaft 52 so that the plates 96 rotatewith the sleeve shaft 52 and are freely axially movable relativethereto. The friction plates 94 and 96 are disposed between annular backand pressure plates 98 and 100, the plates having radial tongues intheir inner peripheries for reception in axial slots in the sleeve shaft52. The pressure plate is hydraulically operated to move axially of theshaft 52 to press the friction plates 94 and 96 together by the back andpressure plates 98 and 100 to drivingly connect the ring gear 68 and sungear 66 and thereby to retard relative rotation of the transmissionshafts 30, 52 and 53 by biasing torque between shaft 52 and cup-shapedmember 76. For this purpose, the pressure plate 100 forms a portion of aservomotor as it is in the shape of a piston receivable within anannular fluid chamber 101 formed in the gear 54; The gear 54 is providedwith a fluid passage 102 connected to an axially extending passage 104in the sleeve shaft 52, the shaft 52 having an annular groove 106communicating with a connected radial and axial passage 108 in shaft 30.The passage 108 is connected to a radial passage 109 adapted to beplaced in communication with another radial passage 110 by the rotaryvalve 64, the passage 110 connecting to another axial passage 114connected to a suitable pressure fluid source (not shown). To controlthe flow of pressure fluid to'the clutch 58, the valve 64 (FIGS. 2 and4) is provided in the shaft 30 and comprises an annular control member116 rotatable on shaft 30 and having spaced ports 118 in its innercylindrical surface and adapted to bridge the radially outer ends of thepassages 109 and 110 in shaft 30, upon rotation of the member 116 toalign the ports 118 and passages 109 and 110 to direct pressure fluidfrom passage 114 to passage 108, groove'106 and passage 104, and thechamber 101 in gear 54 to engage the clutch. The annular member 116 isnormally positioned on shaft 30 to prevent flow of pressure fluid to theclutch 58 and, for this purpose, an annular plate or disc 120 ispositioned on the shaft 30 and engaging one side of the valve member116, the inner periphery of the plate being provided with a collarformed with a laterally extending tongue 122 extending between splinesin the shaft 30 to prevent relative rotation of the disc 120 and shaft30. The disc 120 is provided with a plurality of openings receivingsprings 124, the springs 124 being received within pockets in the sideof the valve member 116 and normally positioning the valve member asshown in FIGS. 2 and 4 to disconnect its ports 1 18 from passages 109and l 10 in shaft 30. When the valve member is forcibly rotated on theshaft 30, the springs can compress sufficiently to permit alignment ofports 118 and passages 109 and but, upon the removal of the force, thesprings expand to again position the valve member 116 as shown.

Control mechanism for the valve 64 and thereby clutch 58 comprises theone-way clutches 60 and 62 operating in response to predetermined speedratios of the input shaft 30 and the sleeve shaft 52 which correspond tospeed ratios between output shafts 50 and 53.

More particularly, the casing is provided with spaced walls 128 and 130having openings receiving a rod 132 for supporting the rod. A wheel 134is rotatable on the rod 132, the rod 132 and valve member 116 eachhaving an annular groove receiving a coil spring belt 136 for drivinglycoupling the rotating valve member 116 to the wheel 134. The wheel 134is formed with a lateral sleeve extending through wheels 140 and 142 andcomprising portions of the conventional one-way clutches 60 and 62, aplurality of rollers 144 and 146 being interposed between and drivinglyengaging the wedging surfaces of the sleeve and wheels 140 and 142. Thewheels 140 and 142 are rotated by coil spring belts 148 and 149respectively positioned in grooves in the wheels 140 and 142 and groovesin the stepped surface of the shaft 52 so that the wheels are rotated bythe shaft 52. The wheel 140 is larger than the wheel 142 and thesewheels are related to the driving wheel 134 that the wheel 140 rotates.88 slower and the wheel 142 rotates 1.02 faster than the wheel 134. Theclutch 60 is oriented so that the wheel 140 may freely overrun thesleeve shaft 52 and its sun gear 66 when the shaft 52 and sun gear 66are rotated faster than the wheel 134 by the shaft 30, the clutchrollers engaging when the shaft 52 rotates the wheel 140 slower than theshaft 30 to couple wheels 134 and 140 for conjoint rotation to createdrag on the valve member 116 to move it to connect ports 118 andpassages 109 and 110 to pressurize the clutch 58. The organization andarrangement of the one-way clutch 62 is such that it will slip or permitfree relative rotation of the wheel 142 and shaft 52 as long as theshaft 30 and wheel 134 rotate faster than the wheel 142 and shaft 52;however, if the shaft 52 rotates faster than the shaft 30, the clutch 62will engage and couple the wheel 142 and wheel 134 to cause belt 136 torotate the valve member 116 to connect ports 118 and passages 109 and110 to direct pressure fluid to the clutch 58.

The operation of the four wheel drive arrangement can best be explainedby initially considering the normal relative speeds of rotation for thevarious components. During level, straight travel, assuming the frontand rear wheels have equal radii and assuming the gear ratios of thefront and rear differentials 18 and are the same, wheel 140 rotatesslower than wheel 134 because of the size differences. In the event oneor both of the front road wheels lose traction and tend to spin freely,the shaft 50 will rotate the gears 56 and 54 to cause the shaft 52 andwheel 140 to rotate faster than the wheel 134 to engage the one-wayclutch 60 thereby rotating wheel 134 faster than shaft 30 to providephase rotation between the valve member 116 and shaft 30 so that thevalve member 134 rotates relative to shaft 30 to direct fluid underpressure to the hydraulic clutch 58, which action thus restrictsoverspeeding over a predetermined amount of shaft 52 relative to shaft30. Conversely, in the event one or both of the rear road wheels losetraction and spin freely, the output. shaft 53 and ring gear 74 willincrease speed causing output shaft 52 to rotate slower than the inputshaft 30 because of the different sizes of wheels 140 and 142,

wheel 142 slowing down until it equals the speed of wheel 134 andthereafter tends to become slower than wheel 134 to cause relative phaserotation between the valve member 116 and input shaft 30 to position thevalve member 116 to connect its ports 118 to passages 110 and 169 tosupply pressure fluid to the servomotor of clutch 58 to engage theclutch to restrict overspeeding of the rear road wheels over apredetermined amount.

DESCRIPTION OF MODIFIED EMBODIMENTOF FIGS. 5 AND 6 FIGS. 5 and 6illustrate another control system for the center differential shown inFIG. 2 including thehydraulically operated friction clutch control ofthe planetary gear set and related input and output shafts. Since thecontrol system of FIGS. 5 and 6 is adapted for the center differentialof FIG. 2, it is believed a description of the control system only willbe satisfactory. Portions ofthe differential in FIG. 5, similar to thatof FIG. 2, are identified by the same numerals but having the suffix a.

The control system of FIGS. 5 and6comprises a-pair of rods 500 and 502,the rod 500 being rotatably mounted in a bearing assembly 504 and oneendof an arcuate actuator 506 (FIG. 6) and the rod 502 being rotatablysupported by a bearing assembly 508'and'the other end of the actuator506, the bearing assemblies 504 and 508 having their outer races fixedin and to ar-' cuate recesses (not shown) in the annular rib 510 of thecasing 46a so as to permit limited rotary movements of.- the bearingassemblies and the rods. relative to the casing for the purpose ofactuating or displacing valve-532 in its housing 526.

Wheels 512, 514 and 516 are positioned on therods 500 and 502, thewheels 512 being fixed to the shafts 500 and 502 and engaging the outersurface of a cylindrical collar 518 secured to the input shaft 30a toprovide a friction drive to rotate the wheels 512. A oneway clutch 520is provided to mount the wheel 514 on the shaft 500 and to permitrotation of the wheel, by;its friction drive connection to shaft 52a, inone direction and'to couple the wheel to the shaft-500 during counterrotation of the shaft 52a in an opposite direction, similar to theaction of one-way clutch 144 in the control shown in FIG. 2. A secondone-way clutch-522 is provided between the wheel 516 and shaft 502 topermit rotation of the wheel 516 upon rotation of the shaft 52a in onedirection and to prevent rotation of the wheel 516w upon rotation ofshaft 52a in an opposite direction, the one-way clutch 522 functioningsimilarly to the one-way clutch 146 in the control system shown in FIG.2.

A valve 524 controls fluid under pressure, supplied from a suitablesource (not shown), to the hydraulic clutch to engage the clutch for thesame purpose described with reference to the control of FIG. 2. Moreparticularly, the valve 524 comprises a valve body 526 having-a passage527 connected tothe pressure fluid source and to two branch passages 528and 530 communicating with a passage 534 having a movable valve member532 reciprocal therein to connect the passage 534 with either thepassage 528 or 530 dependenton the direction of movement of the valvemember, the passage 534 providing fluid under pressure to passages 108ain shaft 30a and passages 104a and 102a in shaft 52a and to the clutch58 to engage the clutch. The valve member 532 is connected to theactuator 506 by a link 536 so that, upon limited rotation of theactuator about the shaft 30a, the link will move the valve member up ordown dependent on the. direction of rotation of the actuator 506.

The operation of the one-way clutches S20 and 522 will now be described.

Since the wheel 514 is larger than the wheel 512, and the wheel 514 and516 are related to and engage the stepped diametrical friction-engagingsurfaces of the shaft 520, the wheel 514 rotates .88 slower and thewheel 516 rotates 1.02 faster than the wheel 518. The one-way clutch 520is oriented so that the wheel 514 may freely overrun the shaft 52a whenthe shaft 520 is rotated faster than the wheel 512 by the shaft 30a, theclutch rollers engaging when the shaft 520 rotates the wheel 512 slowerthan the shaft 300 to couple wheels 512 and 514 for unitary rotation tocreate a drag on the actuator 506 coupled to shafts 500 and 502 to movethe valve member to connect one of the passages 528 or 530 to thepassage 534 to provide fluid under pressure to the friction clutch toengage this clutch. Also, the one-way clutch 522 is operative to permitfree relative rotation of the wheel 516 and shaft 52a whenever the shaft30a and wheel 512 rotate faster than the wheel 516 and shaft 52a;however, if the shaft 52a rotates faster than the shaft 30a, the clutch520 will engage and couple the wheel 514 to the wheel 516 and wheel 512to provide a reaction effective to move the valve member to connect oneof the passages 528 or 530 to the passage 534 to pressurize the frictionclutch to engage the same.

The operation of the control system of FIGS. and 6 is similar to thecontrol system of FIGS. 2, 3 and 4, as should one or both of the frontroad wheels lose traction and tend to spin freely, and referring now toFIG. 2, the shaft 92 will rotate the gears 56 and 54 to cause shaft 52and wheel 514 (FIG. 5) to rotate faster than wheel 512 to engage one-wayclutch 520 and rotate wheel 512 faster than shaft 30a to rotate theactuator 506 to open valve 524 to engage the friction clutch to restrictoverspeeding of shaft 52a relative to shaft 300. On the other hand,should one or both of the rear road wheels lose traction to spin freely,the output shaft 53 will increase speed to cause output shaft 520: torotate slower than input shaft 300 due to the different sizes of wheels514 and S16, wheel 516 slowing down until it equals the speed of thewheel 512, and thereafter rotating slower than wheel 512 to causerotation of the actuator 506 and thereby movement of valve member 532 toopen the valve 524 to engage the friction clutch and to restrictoverspeeding 'of the rear road wheels.

It will be apparent that, as in the control system of FIG. 2, thecontrol system of FIGS. 5 and 6 is effective to provide control meanssensing speed ratio between two of the shafts for activating the clutchin response to said speed ratio being in excess of a predetermined valueto bias torque between two of said shafts, the control means includingthe one-way clutches 520 and 522, and valve 524.

DESCRIPTION OF MODIFIED EMBODIMENT OF FIG. 7

The control system of FIG. 7 functions in a mammer and for the samepurpose as that of FIGS. 2 and 5. However, the control system differs instructure as will now be described.

More particularly, the control system of FIG. 7 comprises rods 702 and704 diametrically spaced in relation to the axis of the input shaft 30band rotatably supported by bearing assemblies 706 and 708 fixedlymounted in an annular rib 710 of the casing. Wheels 712 and 714 arefixed to respective rods 702 and 704 and engage the outer surface of theannular control member 11612 of the valve 64b to be frictionally drivenby the control member due to its connection to the input shaft 30b bythe coil spring 1241; and disc 1201), the valve control member 1166having limited rotational movement relative to shaft 30b to align itsports ll8b with the passages and l09b to direct fluid under pressurefrom passage 114k of shaft 30b to the passage 108b, groove 1061) andpassages 104k of shaft 52b to the servomotor operating the frictionclutch.

A one-way clutch 716 is provided to connect a wheel 718 to the rod 702,and a second one-way clutch 720 connects a wheel 722 to the rod 704. Thewheels 718 and 722 engage and are normally rotatable by the steppeddiametrical friction-engaging surfaces of the shaft 52b. The one-wayclutch 716 permits rotation of the wheel 718 in one direction ofrotation of shaft 52b but couples the wheel 718 to the shaft in theevent the shaft 52b overruns the wheel 718. One-way clutch 720 alsopermits rotation of wheel 722 in the direction of rotation of shaft 52bbut couples the wheel 722 to the shaft when the shaft 52b rotates slowerthan the wheel 722. Whenever either the one-way clutch 716 or 720operate to lock the associated wheel to its shaft, rotation of thewheels 714 will be retarded to cause the valve control member 1161: torotate to one or the other of its positions to direct fluid underpressure to the friction clutch to engage the clutch.

The operation of the control system of FIG. 7 is similar to the controlsystem of FIGS. 2, 3 and 4, since, should one or both of the front roadwheels spin freely, the shaft 92, and, referring to FIG. 2, will rotatethe gears 54 and 56 to cause the shaft 52 and wheel 718 (FIG. 7) torotate faster than wheel 712 to engage oneway clutch 716 and rotatewheel 512 faster than shaft 301; to cause the wheel 712 to rotate thevalve member 1l6b to pressurize and engage the friction clutch to restrict overspeeding of shaft 52b relative to shaft 30b. In the eventshould one or both rear road wheels spin freely, the output shaft 53(FIG. 2) will increase its speed to cause output shaft 52b to rotateslower than input shaft 30b due to the different sizes of wheels 718 and722, wheel 722 slowing down until it equals the speed of the wheel 714,and then rotating slower than wheel 714 to cause the wheel 714 and thevalve member 1161: to rotate to open valve 64b to engage the frictionclutch and thereby restrict overspeeding of the rear road wheels.

DESCRIPTION OF THE MODIFIED EMBODIMENT OF FIG. 8

FIG. 8 illustrates another control system for a center differentialsimilar to FIG. 2 and including the planetary gear set, and hydraulicfriction clutch control of the gear set and related input and outputshafts. As these components of this differential have been previouslydescribed, such components will be identified by similar numerals usedin FIG. 2, but bearing the suffix The control system of FIG, 8 comprisesa pressure fluid-generating device 802 in the form of a positivedisplacement bi-directional pump of the conventional gerator type having(FIG. 9) an inner rotor 804 keyed to the input shaft 300, and an outerrotor 806 rotatable in a housing. The housing comprises a cylindricalend portion 808 surrounding the rotors, and side plates 810 and 812. Theouter rotor 806 is provided with recesses 814 therein adapted to receivethe teeth 816 on the inner rotor 804. As seen in FIG. 9, rotation of therotors in a clockwise direction causes fluid to enter the pump throughthe port 818 in the housing plate 810 and, in a well-known manner, willact in the fluid chambers between the teeth 816 of the inner rotor andthe recesses 814 of the outer rotor to provide fluid under pressure to aport 820 in the housing plate 812. Upon rotation of the rotors in acounterclockwise direction, the rotors are effective to cause fluid toenter the pump through port 820 and to provide fluid under pressure toport 818.

When the input shaft 300 and the output shaft 520 rotate under normalfront and rear wheel traction, the rotors 804 and 806 will be rotatedsubstantially unitarily and the pump will be effective to provide fluidunder pressure to the ports 818 or 820. However, in the event either thefront or rear wheels should lose traction and slip, the shaft 520 willrotate relative to the input shaft 300 to cause relative rotation of thepump elements to provide fluid under pressure to passages 104s and 821,by way of control valve 822 to the servomotor of the clutch 58c to causeits pressure plate piston 824 to engage the clutch plate 94c and 96c tobias torque between the ring and sun gears 68c and 660 of the planetarycenter differential.

The control valve 822 comprises a movable valve element or spool 826 anda coil spring 828 located in a radially extending bore 829 in theservomotor housing 830, a plug closing the outer end of the bore. Thehousing 830 is also provided with a port or orifice 832 connecting thevalve bore 829 with the housing chamber 833, containing the piston 824,and the passage 821 connected to the pump. A vent port 834 is alsoprovided in the housing 830 for flow of pressure fluid from the bore 829in the housing to the oil sump of the differential casing 46c, when thevalve spool is operative to connect the port 832 with the vent 834. Thevalve spool 826 is provided with end lands connected by a conicalportion defining a groove communicating with the orifice 832, theradially outer land closing the vent port 834.

In operation, the valve spool is movable, by centrifugal force, in adirection radially outward of the axis of shaft 520 and, by so doing,causes the valve orifice 832 to provide a certain hydraulic resistanceagainst which the pump creates pressure by forcing fluid to flow throughthe resistance 832 and this pressure is effective to energize the clutchpressure plate piston to engage the clutch to restrict slippage oroverspeeding of the front road wheels.

The valve 822 is used to minimize the effect of the vehicle's speed onthe relation between the speed ratio of front vs. rear wheels to thebiased torque between these two sets of wheels. Without the valve 822,the biased torque between the front and rear sets of wheels will dependon the algebraic difference of speed of these two sets of wheels;however, by adding this valve, the biased torque can be made to dependon their speed ratio. In this respect, it may be noted, by way ofexample, if the input shaft 300 rotates at 10 M.P.H., the frontdifferential shaft 52c will rotate at l 1 MPH. and the rear differentialshaft 53c will rotate at 9.5 M .P.H The difference in rotation of thepump element will be 1 MPH. In such case, the valve 822 operates tocause the valve orifice to have 10 times the resistance, compared with acase where the input shaft rotates at 100 M.P.H., the front shaft 52crotates at l 10 M.P.H., and the rear shaft rotates at M.P.I-I. In eithercase, the pressure generated by the pump will be the same, although thefluid flow of the latter example will be onetenth compared to the firstexample.

DESCRIPTION OF THE EMBODIMENT OF THE INVENTION OF FIGS. 10 AND 11 Thecenter differential and its control system illustrated in FIG. 10 isdesigned for use in a multiple driving axle vehicle, such as a fourwheel drive automotive vehicle shown in FIG. 11. More particularly, thedrive arrangement of the vehicle of FIG. 11 comprises a frame 900supporting an engine 901 connected to a suitable transmission 902through a clutch assembly 903 in conventional manner. The transmission902 is coupled to a connecting shaft 904 by a universal coupling 905,the shaft 904 being connected by a universal coupling 906 to a shaft 907in a casing 908. The casing 908 contains transfer gear mechanism 909connecting the shaft 907 to an input gear 910 (FIG. 1 1) of the centerdifferential 91 1 and its control mechanisms 912 and 913 housed in thecasing 914. The center differential 911 has an output shaft 915 havingone end coupled to a shaft 916 by a universal coupling 917, the oppositeend of the shaft 916 being connected by a universal coupling 918 to therear difi'erential 919 driving the rear road wheels 920 of the vehicle.The center differential has also an output shaft 921 connected by auniversal coupling 922 to one end of a shaft 923, the other end of shaft923 being connected, by a universal joint 924, to the front differential925 connected to the front wheels 926.

Referring now to FIG. 10, the output shaft 921 is rotatably mounted in abearing 927 in the front wall 928 of casing 914 and the output shaft 915is rotatable in a bearing 929 in the rear wall 930 of the casing 914.The inner ends of aligned shafts 921 and 915 are adjacent each other andhave splined thereto bevel gears 931 and 932 meshing with a plurality ofbevel gears 933 rotatably mounted on a differential cross 934 having itsfree end portions extending into apertures in a rotatable differentialhousing 935. The housing 935 has a circular shoulder 936 for mountingthe annular spur gear 910 secured thereto by bolts 937 so that, uponrotation of the gear 910, drive will be transmitted from the input gear910 to the housing 935 and thereby to the cross 934 and bevel gears 933to rotate the gear 931 and output shaft 921 to the front differentialand wheels, and also torotate gear 932 and output shaft 915 to the reardifferential and wheels.

The control mechanism 912 comprises a hydraulitatably supporting thehousing on a bearing 940 mounted on the wall 928 of the casing 914, theouter periphery of the plate 938 having splines intermeshed with splines942 on the cylindrical portion 943 of the clutch housing, which iswelded as at 944 to the annular periphery 945 of the housing. Aplurality of friction discs 946 are supported by the splines 942 forrotation with and movement axially of the cylinder 943. A plurality offriction discs 947 are also nonrotatably se: cured to the annularportion 948 of the clutch by means of splines 949 and are interleavedbetween the friction discs 946. Both the friction discs 946 and 947 areaxially movable relative to the clutch housing to activate the clutch.

The hydraulic clutch servomotor used to engage the clutch discs 946 and947 comprises a clutch cylinder 950, and pressure plate piston 985mounted within and reciprocal in the cylinder 950. The clutch cylinderis provided by body portion 951 having an axially extending annularflange 952 and the annular periphery 945 of the clutch housing 936, thecylinder 950 forming an integral portion of the housing 935. The annularpiston 985 has its outer periphery provided with splines interconnectedwith splines 942 on the cylindrical portion 943 of the clutch housing sothe piston 985 will rotate with the housing and can move axially toengage the friction discs 946 and 947. The cylinder 950 is provided withfluid under pressure to actuate the piston 951 by means of a passage 953extending through the clutch body portion 951 and the housing 935 to anannular groove 954 in the housing and passages 955 and 956 in the outputshaft 915. The axial passage 956 in shaft 915 is connected to a radialpassage 957 adapted to be connected by and through a valve 958 to aradial passage 959 in shaft 915, an axial passage 960 in shaft 915connecting the passage 959 to a radial passage 961 in shaft 915communicating with a groove 962 and passage 963 in the differentialhousing 914, the passage 963 being connected to and conducting pressurefluid from a suitable source.

The valve 958 is similar to the valve 64 shown and described withreference to FIGS. 2, 3 and 4 and accordingly, like numbers will be usedwith the suffix d added. The valve comprises an annular control member 116d rotatable about the shaft 915 within predetermined limits aspermitted by the coil springs 124d and plate 120d, the plate 120a beingkeyed to the shaft 915 to cause the valve member to normally rotate withthe shaft. The. valve member 116d has spaced passages 118d alignablewith and bridgeable over the passages 957 and 959 to provide for flow offluid under pressure from passage 957 to passage 959 and to the clutchservornotor.

- The rotative movement of the valve member 116d relative to shaft 915is automatically controlled by the control mechanism 913, similar to theone-way control mechanism shown in FIG. 2, in that the control meanssenses speed ratio between two of the shafts to activate the clutch inresponse to said speed ratio being in excess of a predetermined value.The control mechanism 913 includes a wheel 964 keyed to a rod 965rotatably supported at opposite ends in the spaced walls 986 and 930 ofthe differential casing 914, one end of the rod being mounted in thewall 930 and urged to eccentric rotation of the adjacent portion of therod by a spring wire 980 to provide frictional engagement of the wheels964, 966 and 967 to their respective shaft lands and to valve 958. Thewheel 964 has its outer periphery frictionally engaging the cylindricalouter surface of the valve member 116d to rotate the same on shaft 915to position its passage 118d in bridging relation to the passsages 957and 959 of shaft 915. A pair of wheels 966 and 967 is positioned on therod 965, and conventional one-way clutches 968 and 969 respectivelyconnect the wheels to the rod for free-wheeling of the wheels on therod, or clutching engagement with the rod in response to speeddifferences of the input gear 910 and output shafts 921 and 915. Thewheels 964, 966 and 967 are of different diameters, the wheel 967 beinglarger than the wheels 964 and 966 and the wheel 964 being larger thanthe wheel 966. The wheels 966 the 967 frictionally engage the steppedsurfaces of the end portion 970 of the rotatable housing 935, which ismounted on a bearing 971 of the wall 966 of the casing 914. The one-wayclutches 968 and 969 are structurally similar to and function like theone-way clutches shown in FIG. 2. The clutches comprise a plurality ofrollers interposed between and drivingly engaging the wedging surfacesof the rod 965 and wheels 966 and 967. The clutch 968 is oriented sothat the wheel 966 may freely overrun the sleeve'portion 981 of thewheel 964 when the input gear 910 is rotated faster than the shaft 915.The clutch rollers engage when the shaft 915 rotates slower than theinput gear 910 to create a drag on the valve member 116d to rotate it toconnect ports 1184 with passages 957 and 959 to pressurize the clutch912. The organization and arrangement of the one-way clutch 969 is thatit free wheels as long as the driving input gear 910 rotates slower thanshaft 915', however, if the shaft 915 rotates faster than the shaftinput gear 910, the clutch will engage and couple the wheel 967 andwheel 964 to cause the wheel 964 to rotate valve member 116d relative toshaft 915 to connect ports 118d and passages 957 and 959 to direct fluidunder pressure to the clutch to activate the clutch. In the operation ofthe four wheel drive arrangement, during level and straight travel ofthe vehicle, assuming the front and rear wheels to be of equal radius,they will have substantially the same angular speed and the front andrear differentials 929 and 919 will rotate at the same speed. in thecontrol system, wheel 967 rotates slower than wheel 964 because of thesize difference. In the event one or both of the rear wheels losetraction and tend to spin freely, the shaft 915 and valve member 116dwill rotate the wheel 964 faster than the wheel 967 to engage theone-way clutch 969 thereby causing wheel 964 to rotate valve member 116dto direct pressure fluid to the friction clutch, activating the frictionclutch, Conversely, if one or both of the front wheels spin freely, theshaft 921 will rotate at increased speed to rotate the gear 932 andshaft 915 at a slower speed causing the wheel 964 to rotate slower thanthe wheel ,966 and thereby effect locking of the one-way clutch 968 toprevent rotation of rod 965 and wheel 964 to thereby rotate valve member116d to provide fluid under pressure to activate the friction clutch.

Throughout the various descriptions of the different multiple drivingaxle vehicle embodiments of the invention, with the exception of HG. 8,it will be assumed that all gears and one-way clutch wheels are rotatingin a direction which corresponds to a forward motion of the vehicle, andthat the pressure supply provided for While the present invention hasbeen described in considerable detail and many modifications have beenshown and described, it should be apparent that other changes,modifications, and adaptations thereof may be made by those skilled inthe art, and it is intended to hereby cover all changes, modifications,and adaptations thereof coming within the scope of the appended claims.

What is claimed is:

1. In an automotive differential having three power transmitting shafts,means for biasing torque between two of said shafts, and control meansdriven by at least two of said power transmitting shafts and associatedwith said biasing means for sensing speed ratio between said two of saidshafts and for activating said biasing means in response to said speedratio being in excess of a pre-determined value.

2. In an automotive differential as defined in claim 1 in which one ofsaid shafts is an input shaft, and the other of said shafts are outputshafts, and said control means includes means rotatable with said shaftand sensing the rotary speeds of the shafts and operative to energizesaid torque-biasing means upon sensing more than a predetermined speeddifference between any two shafts.

3. In an automotive differential as defined in claim 1 wherein saidtorque-biasing means is a friction clutch.

4. In an automotive differential as defined in claim 1 wherein saidtorque-biasing means is a friction clutch, a hydraulic servomotor foroperating said clutch, and a valve actuatable to supply pressure fluidto said servomotor, and said control means is operative to actuate saidvalve.

5. In an automotive differential as defined in claim 2 wherein saidtorque-biasing means includes a hydraulically operated friction clutch,a valve actuatable to supply pressure fluid to said clutch, and saidcontrol means senses the rotary speeds of the shafts and is operative,upon speed difierences between the output shafts, to actuate the valve.

6. In an automotive differential as defined in claim 4 wherein saidvalve is connected to two of said shafts and is operable, upon relativerotation thereof, to an open position to direct pressure fluid to saidfriction clutch.

7. In an automotive differential as defined in claim 4 wherein saidvalve includes a'fluid flow control member connected to said input shaftand rotatable relative thereto, by operation of said control means, tosupply pressure fluid to said clutch.

8. In an automotive differential as defined in claim 4 in which one ofsaid shafts is an input shaft, and the other of said shafts are outputshafts, and wherein torque-transmitting means connect said input shaftto said output shafts, and said torque-biasing means in eludes afriction clutch; and wherein said control means is in spaced relation tosaid torque-transmitting means and is operative to actuate said clutch.

9. In an automotive differential as defined in claim 3 includingdifferential gearing having components respectively connected to saidthree shafts for transmitting torque from said input shaft to saidoutput shafts, and wherein said friction clutch includes engageabledriving and driven members respectively connected to two of saidcomponents.

10. In an automotive differential as defined in claim 3, including aplanetary gear set having a sun gear element, ring gear element,planetary carrier element respectively connected to said three shaftsfor transmitting torque between said shafts and wherein said frictionclutch has engageable driving and driven members respectively connectedto two of said elements.

11. In an automotive differential as defined in claim 4 in which saidcontrol means is-operative to maintain said valve in closed positionwhen said speed ratio is less than a predetermined value and toopen'said valve when said speed ratio exceeds said predetermined value.

12. In an automotive differential as defined in claim 1 wherein saidcontrol means includes a control shaft driven by one of saidpower-transmitting shafts, a control member rotatably supported on saidcontrol shaft and driven by a second of said power-transmitting shafts,one-way clutch means disposed between said control shaft and memberallowing free relative rotation of said control shaft and member in onedirection and coupling said control shaft and member when said controlshaft and member rotate in a second direction to activate saidtorque-biasing means.

13.In an automotive differential as defined in claim 12 wherein saidtorque-biasing means includes a friction clutch, a hydraulic servomotorfor operating said clutch, and a valve actuatable by said control means,upon coupling said control shaft and member, to an open position tosupply pressure fluid to said clutch.

14. In an automotive differential as defined in claim 12 wherein saidpower-transmitting shafts include an input shaft and two output shafts,and torquetransmitting means connect said input shaft to said outputshafts, and said one-way clutch means is in spaced relation to saidtorque-transmitting means and incapable of transmitting torque betweensaid input and output shafts.

15. In an automotive differential as defined in claim 1 wherein saidcontrol means includes a first control shaft driven by a first shaft ofsaid power-transmitting shafts, a first control member rotatablysupported on said control shaft, a second control member rotatablysupported on said control shaft, said control members being driven by asecond control shaft driven by a sec ond shaft of said powertransmitting shafts, a first oneway clutch means disposed between saidfirst control shaft and said first control'member and operable to couplesaid first control shaft and first control member upon overspeeding ofsaid second control shaft, in one direction, relative to said firstpower transmitting shaft, and second one-way clutch means disposedbetween said first control shaft and said second control member andoperable to couple said first control shaft and said second controlmember upon overspeeding of said second control shaft, in a secondopposite direction, relative to said first control shaft.

16. In an automotive differential as defined in claim 15 wherein saidfirst power-transmitting shaft is an input shaft, and the other two ofsaid powertransmitting shafts are output shafts, and a gear set connectssaid input shaft to said output shafts and to said second control shaft.

17. In an automotive differential as defined in claim 15 in which saidtorque-biasing means includes a friction clutch, a hydraulic servomotorfor operating said clutch, and a valve controlling pressure fluid tosaid servomotor, and coupling operation of said first and second one-wayclutch means of said control means activating said valve to directpressure fluid to said servomotor.

18. In an automotive differential as defined in claim 16 in which saidgear set includes relatively rotatable members respectively connected tosaid output shafts, and said torque-biasing means includes a frictionclutch having engageable driving and driven members respectivelyconnected to said gear set members to restrict overspeeding, ovdr apredetermined amount, of either of said output shafts relative to saidinput shaft.

19. In an automotive differential as defined in claim 16 in which saidgear set includes relatively rotatable members respectively connected tosaid output shafts, and said torque-biasing means includes a frictionclutch having engageable driving and driven members respectivelyconnected to said gear set members to restrict overspeeding, over apredetermined amount, of either of said output shafts relative to saidinput shafts, an hydraulic servomotor for engaging said clutch membersand a valve controlling pressure fluid to said servomotor and having avalve member operably connected to and actuatable by said first controlshaft, in response to movement of said first control shaft by said firstand second one-way clutch means.

20. In an automotive differential as defined in claim 1 wherein saidtorque-biasing means includes a friction clutch, and said control meansincludes a pressure fluid-generating device having components relativelyrotatable to provide pressure fluid to activate said clutch.

21. In an automotive differential as defined in'claim 1 wherein saidtorque-biasing means includes a friction clutch, a hydraulic servomotorfor engaging said clutch, and said control means includes a positivedistorque between the output shafts.

1. In an automotive differential having three power transmitting shafts,means for biasing torque between two of said shafts, and control meansdriven by at least two of said power transmitting shafts and associatedwith said biasing means for sensing speed ratio between said two of saidshafts and for activating said biasing means in response to said speedratio being in excess of a pre-determined value.
 2. In an automotivedifferential as defined in claim 1 in which one of said shafts is aninput shaft, and the other of said shafts are output shafts, and saidControl means includes means rotatable with said shaft and sensing therotary speeds of the shafts and operative to energize saidtorque-biasing means upon sensing more than a predetermined speeddifference between any two shafts.
 3. In an automotive differential asdefined in claim 1 wherein said torque-biasing means is a frictionclutch.
 4. In an automotive differential as defined in claim 1 whereinsaid torque-biasing means is a friction clutch, a hydraulic servomotorfor operating said clutch, and a valve actuatable to supply pressurefluid to said servomotor, and said control means is operative to actuatesaid valve.
 5. In an automotive differential as defined in claim 2wherein said torque-biasing means includes a hydraulically operatedfriction clutch, a valve actuatable to supply pressure fluid to saidclutch, and said control means senses the rotary speeds of the shaftsand is operative, upon speed differences between the output shafts, toactuate the valve.
 6. In an automotive differential as defined in claim4 wherein said valve is connected to two of said shafts and is operable,upon relative rotation thereof, to an open position to direct pressurefluid to said friction clutch.
 7. In an automotive differential asdefined in claim 4 wherein said valve includes a fluid flow controlmember connected to said input shaft and rotatable relative thereto, byoperation of said control means, to supply pressure fluid to saidclutch.
 8. In an automotive differential as defined in claim 4 in whichone of said shafts is an input shaft, and the other of said shafts areoutput shafts, and wherein torque-transmitting means connect said inputshaft to said output shafts, and said torque-biasing means includes afriction clutch; and wherein said control means is in spaced relation tosaid torque-transmitting means and is operative to actuate said clutch.9. In an automotive differential as defined in claim 3 includingdifferential gearing having components respectively connected to saidthree shafts for transmitting torque from said input shaft to saidoutput shafts, and wherein said friction clutch includes engageabledriving and driven members respectively connected to two of saidcomponents.
 10. In an automotive differential as defined in claim 3,including a planetary gear set having a sun gear element, ring gearelement, planetary carrier element respectively connected to said threeshafts for transmitting torque between said shafts and wherein saidfriction clutch has engageable driving and driven members respectivelyconnected to two of said elements.
 11. In an automotive differential asdefined in claim 4 in which said control means is operative to maintainsaid valve in closed position when said speed ratio is less than apredetermined value and to open said valve when said speed ratio exceedssaid predetermined value.
 12. In an automotive differential as definedin claim 1 wherein said control means includes a control shaft driven byone of said power-transmitting shafts, a control member rotatablysupported on said control shaft and driven by a second of saidpower-transmitting shafts, one-way clutch means disposed between saidcontrol shaft and member allowing free relative rotation of said controlshaft and member in one direction and coupling said control shaft andmember when said control shaft and member rotate in a second directionto activate said torque-biasing means.
 13. In an automotive differentialas defined in claim 12 wherein said torque-biasing means includes afriction clutch, a hydraulic servomotor for operating said clutch, and avalve actuatable by said control means, upon coupling said control shaftand member, to an open position to supply pressure fluid to said clutch.14. In an automotive differential as defined in claim 12 wherein saidpower-transmitting shafts include an input shaft and two output shafts,and torque-transmitting means connect said input shaft to said outputshafts, and said one-way clutch meaNs is in spaced relation to saidtorque-transmitting means and incapable of transmitting torque betweensaid input and output shafts.
 15. In an automotive differential asdefined in claim 1 wherein said control means includes a first controlshaft driven by a first shaft of said power-transmitting shafts, a firstcontrol member rotatably supported on said control shaft, a secondcontrol member rotatably supported on said control shaft, said controlmembers being driven by a second control shaft driven by a second shaftof said power transmitting shafts, a first one-way clutch means disposedbetween said first control shaft and said first control member andoperable to couple said first control shaft and first control memberupon overspeeding of said second control shaft, in one direction,relative to said first power transmitting shaft, and second one-wayclutch means disposed between said first control shaft and said secondcontrol member and operable to couple said first control shaft and saidsecond control member upon overspeeding of said second control shaft, ina second opposite direction, relative to said first control shaft. 16.In an automotive differential as defined in claim 15 wherein said firstpower-transmitting shaft is an input shaft, and the other two of saidpower-transmitting shafts are output shafts, and a gear set connectssaid input shaft to said output shafts and to said second control shaft.17. In an automotive differential as defined in claim 15 in which saidtorque-biasing means includes a friction clutch, a hydraulic servomotorfor operating said clutch, and a valve controlling pressure fluid tosaid servomotor, and coupling operation of said first and second one-wayclutch means of said control means activating said valve to directpressure fluid to said servomotor.
 18. In an automotive differential asdefined in claim 16 in which said gear set includes relatively rotatablemembers respectively connected to said output shafts, and saidtorque-biasing means includes a friction clutch having engageabledriving and driven members respectively connected to said gear setmembers to restrict overspeeding, ovdr a predetermined amount, of eitherof said output shafts relative to said input shaft.
 19. In an automotivedifferential as defined in claim 16 in which said gear set includesrelatively rotatable members respectively connected to said outputshafts, and said torque-biasing means includes a friction clutch havingengageable driving and driven members respectively connected to saidgear set members to restrict overspeeding, over a predetermined amount,of either of said output shafts relative to said input shafts, anhydraulic servomotor for engaging said clutch members and a valvecontrolling pressure fluid to said servomotor and having a valve memberoperably connected to and actuatable by said first control shaft, inresponse to movement of said first control shaft by said first andsecond one-way clutch means.
 20. In an automotive differential asdefined in claim 1 wherein said torque-biasing means includes a frictionclutch, and said control means includes a pressure fluid-generatingdevice having components relatively rotatable to provide pressure fluidto activate said clutch.
 21. In an automotive differential as defined inclaim 1 wherein said torque-biasing means includes a friction clutch, ahydraulic servomotor for engaging said clutch, and said control meansincludes a positive displacement pump having pumping membersrespectively connected to said two shafts and relatively rotatablethereby to provide fluid under pressure to said servomotor.
 22. In anautomotive differential as defined in claim 21 wherein said threepower-transmitting shafts include an input shaft and two output shafts,said torque-biasing means includes a valve controlling pressure fluidfrom said pump to said servomotor, said valve being responsive tovehicle speed in a manner to minimize the effect of the vehicle speed onthe relation between the spEed ratio of said output shafts to the biasedtorque between the output shafts.